Fiber optic voltage conditioning

ABSTRACT

A fiber optic voltage conditioner, and method therefor, generally relate to voltage conditioning. In such a fiber optic voltage conditioner, there is a laser, and an optical circulator is coupled to receive a light signal from the laser. A controller is coupled to the laser and is configured to generate first control information for wavelength-drift control of the laser. A data acquisition module is coupled to the controller and is configured to generate second control information for the controller for adjustment of the first control information. A photodetector is coupled to the optical circulator to receive a returned optical signal and is coupled to the data acquisition module to provide an analog output signal thereto. The photodetector is configured to generate the analog output signal responsive to the returned optical signal. The data acquisition module is configured to generate the second control information using the analog output signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims benefit of priority toU.S. patent application Ser. No. 14/814,355, filed Jul. 30, 2015, whichclaims the benefit under 35 U.S.C. section 119(e) of U.S. ProvisionalApplication No. 62/062,429, filed Oct. 10, 2014, and U.S. ProvisionalApplication No. 62/031,790, filed Jul. 31, 2014, and the entirety ofeach of the aforementioned provisional and nonprovisional applicationsis hereby incorporated by reference herein for all purposes consistentherewith.

STATEMENT OF GOVERNMENT INTEREST

The technical feasibility of using claimed technology with an energyharvester for helicopter rotors was demonstrated with government supportunder Phase I SBIR contract number N68335-13-C-0318, “Energy Harvesting,Wireless Structural Health Monitoring for Helicopter Rotors”.Accordingly, the technology claimed herein existed before entry into theSBIR contract; however, the U.S. Government may have certain rights inother technology, if any, developed pursuant to the terms of such PhaseI SBIR contract.

FIELD

The following description relates generally to voltage, includingsignal, conditioning. More particularly, the following descriptionrelates to fiber optic voltage conditioning for sensor integration.

INTRODUCTION

For real-time structural health monitoring, conventional strainmeasurement instrumentation may be used with conventional voltage orsignal conditioners. However, such conventional signal conditioners maynot have sufficient performance for some structural health monitoringapplications. Along those lines, optical sensors may be used for somestructural health monitoring applications involving such performancedemands. Use of optical sensors may involve fiber optic voltageconditioning. However, conventional fiber optic voltage conditioning maybe too expensive or too heavy for some real-time structural healthmonitoring applications.

BRIEF SUMMARY

A fiber optic voltage conditioner generally relates to voltageconditioning. In such a fiber optic voltage conditioner, there is alaser, and an optical circulator is coupled to receive a light signalfrom the laser. A controller is coupled to the laser and is configuredto generate first control information for wavelength-drift control ofthe laser. A data acquisition module is coupled to the controller and isconfigured to generate second control information for the controller foradjustment of the first control information. A photodetector is coupledto the optical circulator to receive a returned optical signal and iscoupled to the data acquisition module to provide an analog outputsignal thereto. The photodetector is configured to generate the analogoutput signal responsive to the returned optical signal. The dataacquisition module is configured to generate the second controlinformation using the analog output signal.

A method generally relates to fiber optic voltage conditioning. In sucha method, a light signal is generated with a laser. The light signal isreceived by an optical circulator. First control information isgenerated by a controller coupled to the laser for wavelength-driftcontrol of the laser. Second control information is generated by a dataacquisition module coupled to the controller. The first controlinformation is adjusted by the controller responsive to the secondcontrol information. A returned optical signal is received by aphotodetector coupled to the optical circulator. An analog output signalis generated by the photodetector responsive to the returned opticalsignal. The generating by the data acquisition module of the secondcontrol information is for the analog output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Accompanying drawing(s) show exemplary embodiment(s) in accordance withone or more aspects of the invention; however, the accompanyingdrawing(s) should not be taken to limit the invention to theembodiment(s) shown, but are for explanation and understanding only.

FIG. 1 is a block diagram depicting an exemplary single-channel lasertracking-based fiber optic voltage conditioning (“FOVC”) system.

FIGS. 2A and 2B are block diagrams depicting an exemplary reflectionfiber extender system and an exemplary transmission fiber extendersystem, respectively.

FIG. 3 is a block diagram depicting an exemplary multichannel FOVCsystem.

FIG. 4A is a block diagram depicting an exemplary wavelength-multiplexedmultichannel FOVC system in a ring configuration.

FIG. 4B is a block diagram depicting an exemplary wavelength-multiplexedmultichannel FOVC system in a star configuration.

FIG. 5 is a block diagram depicting an exemplary fiber optic strainvoltage conditioner system.

FIG. 6 is a flow diagram depicting an exemplary fiber optic voltageconditioning flow.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of theinvention and is not intended to represent the only embodiments in whichthe invention may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof the invention. However, it will be apparent to those skilled in theart that the invention may be practiced without these specific details.In some instances, well known structures and components are shown inblock diagram form in order to avoid obscuring the concepts of theinvention. In other instances, well-known features have not beendescribed in detail so as not to obscure the invention. For ease ofillustration, the same number labels are used in different diagrams torefer to the same items; however, in alternative embodiments the itemsmay be different. Furthermore, though particular dimensions, parameters,and other numerical details are described herein for purposes of clarityby way of example, it should be understood that the scope of thedescription is not limited to these particular numerical examples asother values may be used.

Exemplary apparatus(es) and/or method(s) are described herein. It shouldbe understood that the word “exemplary” is used herein to mean “servingas an example, instance, or illustration.” Any example or featuredescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other examples or features.

A structural health monitoring system capable of measuring load,vibration, and/or acoustic emission (“AE”) responses corresponding todamages occurring in materials and/or structures is described. Such asensing system may include a fiber Bragg grating (“FBG”) sensor arrayinterrogated by laser-based detection system. Such a laser-baseddetection system in an example may be a miniaturized stand-alonelaser-based detection system.

In an implementation, such a structural health monitoring system may becombined with a multichannel wireless data acquisition node andhigh-performance energy harvesters, the feasibility of which wasdemonstrated under the above-identified Phase I SBIR contract. Alongthose lines, in an example implementation, a load and damage monitoringsystem for helicopter blades was developed using such a low weight,high-speed structural health monitoring (“SHM”) system, as described inadditional detail below. Such additional description of such SHM systemwith examples of helicopter blades, though wind turbine blades or otherrotating objects may be used, using fiber optics (“FO”), includingwithout limitation fiber optic acoustic emission (“FOAE”) monitoring isprovided; however, it should be understood that such SHM system is notlimited to the application of monitoring helicopter blades, but may beused in other applications. Along those lines, such FOAE monitoring maybe used to monitor for corrosion damage, metal fatigue, compositedamage, concrete micro-fracture, wire break, and/or pipe damage, amongother examples.

FIG. 1 is a block diagram depicting an exemplary single-channel lasertracking-based fiber optic voltage conditioning system 100. In order toprovide voltage conditioning for acoustic emissions (“AEs”)measurements, an open/closed loop control 101 of fiber optic voltageconditioner (“FOVC”) 110 of fiber optic voltage conditioning system 100may be used to actively track a laser to Bragg wavelength of an FBGsensor.

A function of laser tracking-based FOVC 110 may be to provide fiberoptic voltage conditioning of returned optical signal 103 coupled to FBGsensors (collectively and singly “FBG sensor”) 111 via a fiber opticcable or line, as described below in additional detail. Along thoselines, a multifunction fiber optic sensor, such as fiber Bragg gratingsensor, may be used. For AE measurements, using a fiber Bragg gratingsensor in a fiber optic housing, an entire sensing area can be bondeddirectly to a surface of a structure (“measurement surface”) such aswith a permanent epoxy or other bonding material. The direct bonding ofa bare fiber to a measurement surface may provide a high-level of stresswave coupling from such measurement surface to a sensing area.

However, over time such bonding material may result in local stressalong such Bragg grating sensor, such as along a grating length forexample, and this may lead to creation of an unstable optical cavityformed by multiple gratings, such as along such grating length forexample. These optical cavities may negatively affect FOAE sensorperformance by changing the slope of a Bragg reflection spectrum and/orincreasing Fabry-Perot noise. To address this issue, an overhangingridge configuration may be used, where a grating under tension may beused for hanging over two stand-offs bonded to a structure's surface toaddress the above-described problem, such as for AE and/or strainsensing. Moreover, for an overhanging ridge configuration, a grating maybe used for hanging over shear wave-coupling gel, on either or bothsides thereof, to provide a flexible bonding to a structure's surface toaddress the above-described problem, such as for AE and/or temperaturesensing. Optionally, a package sensor multiplexing two or more FBGsensors on the same package with different Bragg wavelengths installedcan be multiplexed in serial or parallel. Such a package sensor may beused for AE, strain, and/or temperature sensing. Moreover, optionally amultiplexed-multi-sensing package sensor may be used. For example, twoor more different types of sensors (e.g., AE/strain and AE/temperature)can be multiplexed on the same package for multi-sensing.

Another function of such laser tracking-based FOVC 110 may be to convertreturned optical signal 103 from FBG sensor 111 to an AC voltage analogoutput 105 that may directly interface with conventional AEinstrumentation, which is illustratively depicted as AE data acquisitionsystem 130. An analog signal output 105 of FOVC 110 may resemble that ofa piezo-electric sensor used in conventional AE measurements,facilitating sensor “drop in replacement”.

Along those lines, conventional piezo-electric sensors/preamplifiersignal conditioners can be completely replaced with a combination of FBGsensor 111 and FOVC 110 as described herein without changing existing AEsoftware and electronics of conventional AE data acquisition systems,such as AE data acquisition system 130 for example, leading tosignificant cost saving through minimizing additional hardware/softwareinstallation. In other words, a high-frequency, high-gain photodetectoroutput 105 carrying a high frequency signal may be interfaced directlyto an analog input of a conventional AE data acquisition system 130,such as a Mistras PCI-2 DAQ board from Mistras Group, Inc. of PrincetonJunction, N.J., for example.

Light 104, which may be from a compact, commercially availabledistributed feedback (“DFB”) laser or other laser 112, may be passed viaan optical circulator 113 to an FBG sensor 111. A returned opticalsignal 103 from FBG sensor 111 passing through optical circulator 113may be routed to a photodetector 114. Current control 116, which may beseparate from or part of DFB laser 112, may be initially set at amidrange value between a lasing threshold and a maximum current limit,and a thermoelectric cooler (“TEC”) control 115, which may be separatefrom or part of DFB laser 112, may be tuned to move laser wavelength toa mid-reflection point (“V REF”) of a Bragg wavelength of FBG sensor111.

With laser current and TEC control voltages settled at initial setpoints, namely V TEC SET and V CUR SET 121, laser wavelength may belocked to a mid-reflection point of FBG sensor 111 using simultaneousTEC and current tracking through a closed loop 101proportional-integral-derivative (“PID”) feedback control.

For adjustment for real-time laser tracking control, a chip-based dataacquisition (“DAQ”) board 120, such as an FPGA-based or otherSystem-on-Chip-based (“SoC-based”) circuit board, may be used to recordat least one of a low-gain and/or low-frequency of photodetector outputsignal 106, namely as associated with an analog input toanalog-to-digital converter (“ADC”) 117 and to generate a PID controlsignal 107, namely as associated with a digital output of ADC 117.

By “low-gain” and “low-frequency”, it is generally meant an analogoutput signal being below both a threshold gain and a thresholdfrequency, respectively, where such thresholds represent an externalenvironmental change and/or perturbation, including without limitation achange in one or more of temperature, strain, pressure, and/or stress ofa structure under test, including a structure being monitored, as sensedby one or more FGB sensors coupled to one or more optical fibers.Accordingly, such thresholds may vary from application-to-applicationdepending upon the type of structure being tested, as well as use ofsuch structure.

An analog output signal 106 of photodetector 114 may be converted to adigital signal by ADC 117, and output of ADC 117 may feed an input of avoltage set and store block 119. An output of voltage set and storeblock 119 may feed an input of DAC 118 to provide an analog PID controlsignal 107. PID control signal 107 may include a PID current error (“CURERR”) signal and a PID TEC error (“ERR”) signal. PID control signal 107may be output from DAC 118.

For purposes of clarity by way of example and not limitation, it shallbe assumed that an FPGA is used to set and store voltages; however, inanother implementation another type of SoC may be used, includingwithout limitation an ASSP, ASIC, or other IC. Along those lines,voltage set and store block (“FPGA”) 119 may be used to set and store alaser current voltage and a TEC control voltage, namely V TEC SET and VCUR SET 121, and FPGA 119 may be used to store a mid-reflection point VREF of a Bragg wavelength of FBG sensor 111. FPGA 119 may be coupled toreceive a digital output 123 from ADC 117, where such digital output 123is a conversion of an analog photodetector output signal 106. FPGA 119may be configured to generate and store TEC and laser current errorvoltages, namely a V TEC ERR and a V CUR ERR, using such digital output123 received. FPGA 119 may provide a digital PID control signal 124,where such digital PID control signal includes a V CUR ERR signal and aV TEC ERR signal, to DAC 118, and DAC 118 may convert such digital PIDcontrol signal 124, namely a V TEC ERR signal and a V CUR ERR signal, toanalog PID control signal 107 having analog PID CUR ERR and PID TEC ERRsignals.

PID CUR and TEC error signals from PID control 107 may becorrespondingly added to CUR and TEC set voltages 121 by adder 122, andrespective sums 108 output from adder 122 may be fed into a controller150 for adjustment of control information provided to laser 112. In thisexample, for purposes of clarity and not limitation controller 150 isbroken out into three controllers or modules, namely a laser controller153 coupled to a current controller 116 and a TEC controller 115.However, in another implementation, current controller 116 and/or TECcontroller 115 may be part of a laser, such as DFB laser 112 forexample. Sums 108 may be used together to compensate for drift of aBragg wavelength, such as due to external environmental changes and/orperturbation including without limitation changes in one or more oftemperature, strain, pressure, and/or stress, by actively tuning laserwavelength responsive to such current and TEC control.

In this example, both laser TEC and current are used simultaneously tocompensate for FBG wavelength drift from DC up to approximately 20 kHzfor photodetector output signal 106. TEC tracking may be provided bychanging temperature of DFB laser 112 via TEC control 115 to compensatefor FBG sensor 111 wavelength drift caused by environmental changes.While providing large dynamic range, such as for example approximatelyseveral thousand microstrains for strain monitoring, TEC compensationmay be slow, with a maximum response time in the order of seconds orlonger.

In this example, fast, such as for example a few Hz to 20 kHz or higher,real time compensation may not be possible with TEC tracking. Alongthose lines, laser current compensation, as described herein, may beused with a much higher response time, possibly up to approximately 20kHz or higher, subject to limitations of response time of electronics oflaser controller 153, and such laser current compensation may be usedsimultaneously with TEC tracking. Tracking by changing laser injectioncurrent may cause changes in both laser wavelengths and intensity,although with much more limited dynamic range, such as for exampleapproximately several hundred microstrains for dynamic strain tracking.For larger dynamic strain monitoring, such as more than approximately athousand microstrains, commercially available distributed Braggreflector (“DBR”) lasers can be used in place of DFB lasers. However, itshould be appreciated that using TEC and current tracking in combinationprovides extended dynamic range and fast response for laser tracking.

Long-distance AE measurement using a laser-based FBG interrogation maybe subject to presence of high amounts of optical noise associated withthe Fabry-Perot effect generated by an optical cavity created by two ormore reflective mirrors. By “interrogation,” it is generally meantproviding a light signal to an optical sensor coupled to a material orstructure under test and obtaining a light signal in return from suchoptical sensor to obtain information therefrom regarding such materialor structure under test. A Bragg grating itself may be considered ahighly reflective mirror. In the presence of another reflective surfacefrom an optical component, such as for example an optical circulator ora scattering center such as a local defect present in a long opticalfiber, unstable, unwanted constructive optical interferences can begenerated due to laser coherence. Accordingly such interferences maycontribute to increased AE background noise, and as a consequence cansignificantly reduce a signal-to-noise ratio (“SNR”) in AE measurements.

To suppress this optical noise, a combination of circulators and opticalisolators between reflection and/or scattering surfaces may be used toprovide unidirectional optical paths and avoid bidirectional opticalpaths between any two reflective optical components, such as describedbelow in additional detail.

FIG. 2A is a block diagram depicting an exemplary reflection fiberextender system 200A, and FIG. 2B is a block diagram depicting anexemplary transmission fiber extender system 200B. One or more instancesof each of fiber extender systems 200A and 200B may be used separatelyfrom one another or a combination of such systems may be used.Accordingly, reflection fiber extender system 200A and transmissionfiber extender system 200B are generally referred to hereinbelow as“fiber extender system 200”, and correspondingly reference to either orboth FIGS. 2A and 2B hereinbelow is generally to “FIG. 2”.

Fiber extender system 200 may include a reflection fiber extender 201coupled between an FOVC 110-1 and a FBG sensor 111-1 and/or atransmission fiber extender 202 coupled between an FOVC 110-2 and a FBGsensor 111-2. Fiber extender system 200 may be used for long distance AEmeasurements.

Fiber extenders 201 and 202 may respectively be used in a reflection anda transmission mode. Reflection fiber extender 201 may include two longoptical fibers 210 and 211 coupled between optical circulators 213-1 and213-2. Transmission fiber extender 202 may include a long optical fiber220 coupled between an optical circulator 213-3 and an optical isolator231-1, and may include another long optical fiber 221 coupled between anoptical isolator 231-2 and optical circulator 213-3.

Along those lines for a reflection mode, light 104 passed throughcirculator 113 of FOVC 110-1 may be passed through circulator 213-1 foroptical fiber 210. Optical fiber 210 may conduct light 104 to circulator213-2 for output therefrom to FBG sensor 111-1. Responsive towavelengths in such light 104, including without limitation isolatingone or more perturbations in such light, a returned optical signal 103from FBG sensor 111-1 may be provided to circulator 213-2. Along thoselines, FBG sensor 111-1 may reflect one or more wavelengths in suchlight 104 for generating returned optical signal 103, and FBG sensor111-1 may transmit one or more other wavelengths in such light 104 foreffectively blocking or filtering out such transmitted wavelengths frombeing included in returned optical signal 103. Circulator 213-2 mayprovide returned optical signal 103 to circulator 213-1 via opticalfiber 211. Lastly, circulator 213-1 may provide such returned opticalsignal 103 to circulator 113 of FOVC 110-1 for processing as previouslydescribed herein.

For a transmission mode, light 104 passed through circulator 113 of FOVC110-2 may be passed through circulator 213-3 for optical fiber 220.Optical fiber 220 may conduct light 104 to optical isolator 231-1 foroutput therefrom to FBG sensor 111-2. Responsive to wavelengths in suchlight 104, including without limitation isolating one or moreperturbations in such light, a returned optical signal 103 from FBGsensor 111-2 may be provided to optical isolator 231-2. Along thoselines, FBG sensor 111-2 may reflect or block one or more wavelengths insuch light 104 for effectively blocking or filtering out same from areturned optical signal 103, and FBG sensor 111-2 may transmit one ormore other wavelengths in such light 104 for generating returned opticalsignal 103. Optical isolator 231-2 may provide returned optical signal103 to circulator 213-3 via optical fiber 221. Lastly, circulator 213-3may provide such returned optical signal 103 to circulator 113 of FOVC110-2 for processing as previously described herein.

FIG. 3 is a block diagram depicting an exemplary multichannel FOVCsystem 300. Multichannel FOVC system 300 is further described withsimultaneous reference to FIGS. 1 through 3.

In multichannel FOVC system 300, an N-channel FOVC 110M is respectivelycoupled to FBG sensors 111-1 through 111-N via corresponding opticalcirculators 113-1 through 113-N, for N a positive integer greater thanone. FBG sensors 111-1 through 111-N may be respective discrete FOAEsensors or an array thereof.

DFB1 through DFBN lasers 112-1 through 112-N and correspondingphotodetectors (“PD”) PD1 114-1 through PDN 114-N may be respectivelycoupled to optical circulators 113-1 through 113-N. Each of DFB lasers112-1 through 112-N may deliver corresponding laser lights 104-1 through104-N respectively into Bragg grating sensors 111-1 through 111-N viacorresponding circulators 113-1 through 113-N. Circulators 113-1 through113-N may then be used to pass corresponding returned optical signals103-1 through 103-N respectively from sensors 111-1 through 111-N on aper channel basis. Returned optical signals 103-1 through 103-N may berespectively provided onto photodetectors 114-1 through 114-N.

Each of the outputs of photodetectors 114-1 through 114-N, which may beimplemented in an example implementation as photodiodes (“PD”) PD1through PDN, may be split into two sections, namely signals 106-1through 106-N and signals 105-1 through 105-N. One group, namely a lowfrequency signal output group of signals 106-1 through 106-N, may beinput into an analog input interface 301, such as respective analoginput ports for example, of an FPGA-based data acquisition system 120for laser tracking control generation as previously described herein.Another group, namely a high frequency signal output group of signals105-1 through 105-N, may be input to a conventional multichannel AE DAQsystem 130 for AE measurement.

Even though an FPGA 119 is used as described herein for DAQ 120, anothertype of SoC, an ASSP, an ASIC, or other VLSI type of integrated circuitdevice may be used instead of FPGA 119. However, for purposes of clarityand not limitation, it shall be assumed that an FPGA 119 is used.Furthermore, DAC 120 may exist in a single integrated circuit device,whether such device is a monolithic integrated circuit or an integratedcircuit formed of two or more integrated circuit dies packaged together.An FPGA 119 may have sufficient resources for integration of one or moreADCs 117, one or more DACs 118, and/or one or more adders 122 thereinfor providing a multichannel FOVC 110M. However, an FPGA may lacksufficient analog resources, and so a separate analog chip, such as forproviding digital-to-analog conversions, may be used.

In this example, FOVC 110M includes a DAQ 120 having an FPGA 119configured for inputs 1 through N of an analog input interface 301(“inputs 301”) and outputs 1 through 2N of an analog output interface302 (“outputs 302”), for example separate analog output ports. Inputs301 may correspond to a group of signals 106-1 through 106-N. Pairs ofoutputs 108-1 through 108-N of outputs 302 may respectively be providedto laser controllers 153-1 through 153-N. Laser controllers 153-1through 153-N may provide respective pairs of TEC and current controlsignals 115-1, 116-1 through 115-N, 116-N to DFBs 112-1 through 112-N,respectively. For purposes of clarity by way of example and notlimitation, laser controllers 153-1 through 153-N are illustrativelydepicted as including corresponding pairs of current and TECcontrollers, which were illustratively depicted as separate controllers116 and 115, respectively, in FIG. 1 for purposes of clarity. However,it should be understood that controllers 115 and 116 may be incorporatedinto a laser controller 153.

Accordingly, for purposes of scaling an FOVC 110, it should beappreciated that a single FPGA 119 may be used by a DAQ 120 configuredto support N channels. In this example, FOVC 110M does not includeoptical circulators 113-1 through 113-N; however, in anotherconfiguration, FOVC 110M may include optical circulators 113-1 through113-N.

Generally, FPGA 119 generates respective sets, such as pairs forexample, of TEC and current control signals 108-1 through 108-N viaanalog output ports 302 of DAQ 120, and such respective sets of TEC andcurrent control signals 108-1 through 108-N may be used to providecorresponding pairs of TEC control and current control signals 115-1,116-1 through 115-N, 116-N to respectively lock DFB lasers 112-1 through112-N to their respective FBG sensors 111-1 through 111-N by addingrespective error signals. Such respective error signals may be generatedfrom FPGA 119 generated PID control to provide current and TEC setpoints via digital summing as previously described herein, though on aper-channel basis in this example of FOVC 110M. For long distancemeasurements, N fiber extenders, whether all transmission fiberextenders 202, all reflection fiber extenders 201, or a combination offiber extenders 201 and 202, as previously described with reference toFIG. 2 may be used in conjunction with multichannel FOVC 110M.

FIG. 4A is a block diagram depicting an exemplary wavelength-multiplexedmultichannel FOVC system 400 having a ring configuration.Wavelength-multiplexed multichannel FOVC system 400 includes FOVC 110Mof FIG. 3, without optical circulators 113-1 through 113-N, coupled to aring multiplexer 410. Wavelength-multiplexed multichannel FOVC system400 may be used for wavelength-multiplexed N-channel fiber optic voltageconditioning for FOAE measurement configured in a ring topology.

FBG sensors 111-1 through 111-N are FOAE sensors with Bragg reflectionwavelengths for a wavelength range, which may vary fromapplication-to-application. For example, such wavelengths may be in arange of approximately 1510 nm to 1650 nm. For purposes of clarity byway of example and not limitation, it shall be assumed that suchwavelengths include 1510 nm and 1650 nm.

FOVC 110M is coupled as previously described to provide laser light104-1 through 104-N and to receive returned optical signals 103-1through 103-N. Accordingly, description of FOVC 110M is generally notrepeated for purposes of clarity and not limitation.

In a ring topology, FBG sensors 111-1 through 111-N may be connected inseries, and a ring multiplexer 410 may be used to provide laser trackingin a transmission mode. In a ring multiplexer 410, a wavelength divisionmultiplexing multiplexer (“WDM mux”) 401 may be configured to multiplexN DFB laser light outputs 104-1 through 104-N into a single modemultiplexed optical signal 441 for providing to a single-modetelecommunication fiber 440.

Telecommunication fiber 440 may include N FBG sensors 111-1 through111-N coupled in series. Telecommunication fiber 440 may include opticalisolators 231-0 and 231-N respectively bracketing such series of FBGsensors 111-1 through 111-N, and may include optical isolators 231-1through 231-(N−1) respectively inserted between each adjacent pair ofFBG sensors of such series of FBG sensors 111-1 through 111-N.Optionally, an optical isolator 231-N may be separated out to be moreproximate to an input of a WDM demultiplexer (“demux”) 402 of ringmultiplexer 410 for providing a returned multiplexed optical signal 442output from telecommunication fiber 440 after processing such singlemode multiplexed optical signal 441.

More generally, an optical isolator 231 may be inserted between eachoptical component and/or FBG sensor to provide unidirectional opticalpaths, namely overall a single unidirectional ring path of ringmultiplexer 410, and to suppress cavity-like optical noises. Along thoselines, input optical isolators 431-1 through 431-N of ring multiplexer410 may respectively be coupled to receive laser lights 104-1 through104-N and to provide optically isolated version thereof as respectiveinputs to WDM mux 401, and output optical isolators 432-1 through 432-Nof ring multiplexer 410 may respectively be coupled to receivedemultiplexed returned optical signals 103-1 through 103-N from WDMdemux 402 to generate optically isolated version thereof as respectiveinputs to photodetectors of FOVC 110M as previously described.

WDM demux 402 of ring multiplexer 410 may be coupled to receive returnedmultiplexed optical signal 442 and configured to demultiplex suchoptical signal into transmitted signals passed through FBG sensors andoptical isolators onto N separate photodiodes 114-1 through 114-N, aspreviously described.

FIG. 4B is a block diagram depicting an exemplary wavelength-multiplexedmultichannel FOVC system 490 having a star configuration.Wavelength-multiplexed multichannel FOVC system 490 includes FOVC 110Mof FIG. 3, without optical circulators 113-1 through 113-N, coupled to astar multiplexer 450. Wavelength-multiplexed multichannel FOVC system490 may be used for wavelength-multiplexed N-channel fiber optic voltageconditioning for FOAE measurement configured in a star topology.

FBG sensors 111-1 through 111-N may be FOAE sensors with Braggreflection wavelengths as previously described. FOVC 110M is coupled aspreviously described to provide laser light 104-1 through 104-N and toreceive returned optical signals 103-1 through 103-N. Accordingly,description of FOVC 110M is generally not repeated for purposes ofclarity and not limitation. FOAE measurement may be performed in areflection mode with N FBG sensors 111-1 through 111-N connected inparallel using N-channel FOVC 110M coupled to a star multiplexer 450 ofwavelength-multiplexed multichannel FOVC system 490.

A star multiplexer 450 includes an optical mux/demux device 460 coupledto an optical demux/mux device 470 via an optical cable, such as abidirectional optical fiber 420. Mux/Demux device 460 includes a WDM mux401, a WDM demux 402, input optical isolators 431-1 through 431-N, andoutput optical isolators 432-1 through 432-N, as previously described,except that mux/demux device 460 further includes an optical circulator413-1 coupled as described below.

WDM mux 401 multiplexes N DFB laser light outputs 104-1 through 104-Ninto a single-mode multiplexed optical signal 441 for providing tooptical circulator 413-1 of optical mux/demux device 460. Suchsingle-mode multiplexed optical signal 441 may be output from opticalcirculator 413-1 into a single-mode telecommunication optical fiber 420.Optical mux/demux device 460 may be used to multiplex N DFB laseroutputs via such an N×1 multiplexer. Optical circulator 413-1 may becoupled to optical fiber 420 to provide such single-mode multiplexedoptical signal 441 to optical demux/mux device 470 and to receivereturned light, namely a returned multiplexed optical signal 442. Such areturned multiplexed optical signal 442 may be demultiplexed into Nrespective photodiode inputs via a 1×N demultiplexer, such as WDM demux402 as previously described.

Demux/Mux device 470 may be used to demultiplex multiplexed light, suchas multiplexed optical signal 441, from mux/demux device 460 into Nseparate outputs for N FBG sensors 111-1 through 111-N coupled forreflection modes. Along those lines, an optical circulator 413-2 ofdemux/mux device 470 may be coupled to optical fiber cable 420 toreceive multiplexed optical signal 441 for providing to a WDM demux 472of demux/mux device 470.

Such a 1×N WDM demux 472 may provide N demultiplexed optical signalsrespectively to optical circulators 473-1 through 473-N of demux/muxdevice 470. Such demultiplexed optical signals may be respectivelyprovided to such separate FBG sensors 111-1 through 111-N coupled forcorresponding reflection modes. FBG sensors 111-1 through 111-N may beexternally (as illustratively depicted) or internally coupled to starmultiplexer 450.

In response to such demultiplexed optical signals, FBG sensors 111-1through 111-N may respectively generate reflected returned opticalsignals to optical circulators 473-1 through 473-N. Optical circulators473-1 through 473-N may be coupled to WDM mux 471 of demux/mux device470 to respectively provide such returned light signals from FBG sensors111-1 through 111-N. WDM mux 471 may multiplex such returned lightsignals to provide a returned multiplexed optical signal 442 to opticalcirculator 413-2. Such returned multiplexed optical signal 442 may beprovide by optical circulator 413-2 into optical fiber cable 420 foroptical circulator 413-1, and optical circulator 413-1 may provide suchreturned multiplexed optical signal 442 to WDM demux 402 fordemultiplexing, as previously described.

In another configuration, mux/demux device 460 may be integrated intoFOVC 110M to provide a single optical interface. Along those lines,optical fiber cable 420 and demux/mux device 470 may be used as anexternal device connected to individual FBG sensors. For long distancemeasurements, such optical fiber 420 may be replaced by a reflectionfiber extender, as previously described herein, to suppress opticalnoise.

FIG. 5 is a block diagram depicting an exemplary fiber optic strainvoltage conditioner system 500. Fiber optic strain voltage conditioning(“FOSVC”) system 500 may be configured to convert optical signals fromFBG sensors 111 into analog voltage outputs 501 that may be directlyinterfaced with conventional strain instrumentation, as described belowin additional detail. Strain-induced wavelength shifts experienced byone or more of FBG sensors 111 may be converted to analog voltagesignals (“analog output”) 502 that resemble parametric outputs of aconventional strain gauge signal conditioner. This allows FOSVC system500 to work as a high-performance “drop-in” replacement for a signalconditioner in conventional strain measurement systems, as describedbelow in additional detail.

FOSVC system 500 includes an FBG Analyzer (“FBGA”) module 510, aSystem-on-Chip (“SoC”) module 520, FBG sensors 111 in an optical fiber501, an optical fiber-to-structure bonding material 504, and adigital-to-analog (“D/A”) converter 530. Optionally, FOSVC system 500may be coupled to a network 590, which may include the Internet, forcloud storage 591. Optionally, one or more web-browser enabled devices592 may be used to communicate with such cloud storage 591 via suchnetwork 590.

FBG sensors 111 in an optical fiber 501 housing may be coupled toreceive and provide an optical signal via such optical fiber 501, theformer of which is for optical transmission of light from broadbandlight source 505. A bonding material 504 may be used to couple opticalfiber 501 of FBG sensors 111 to a material or structure under test 503.A broadband light source 505, such as an LED light source, of FBGAmodule 510 may provide light to an optical circulator 506 of FBGA module510, and such light may be sent through to optical fiber 501 via passingthrough optical circulator 506 through to FBG sensors 111. Responsive tostrain-induced wavelength shifts experienced by one or more of FBGsensors 111, any reflected light from FBG sensors 111 may be provided asoptical signals via optical fiber 501 to optical circulator 506 forspectral element 507 of FBGA module 510.

Reflected light may be spectrally dispersed through spectral element507, which in this example is a Volume Phase Grating (“VPG”) element 507of FBGA module 510. Such dispersed light may be detected by a photodiodearray 508 of FBGA module 510, which in this example is an Indium GalliumArsenide (InGaAs) photodiode array; however, other types of photodiodearrays may be used in other implementations. Outputs of photodiode array508 may be digitized using an analog-to-digital converter (“A/Dconverter”) 509 of FBGA module 510. Output of A/D converter 509 may bepacketized by an on-board integrated circuit packetizer 511 of FBGAmodule 510, which in this example is separate from an FPGA of SoC module520. However, in another implementation, packetizer 511 and/or A/Dconverter 509 may be implemented in an FPGA of SoC module 520. Suchpacketized information may be forwarded from packetizer 511 to SoCmodule 520 for post-processing.

SoC module 520 may include CPU complex 521, a programmable gate arraydevice 522, and main memory 523. In this example, such programmable gatearray device 522 is an FPGA; however, in other implementations, othertypes of integrated circuits, whether programmable gate array devices ornot, may be used to provide a D/A interface 524 and digital signalprocessing (“DSP”) hardware 525.

CPU complex 521, which may be on a same FPGA as D/A interface 524 andDSP hardware 525 in another implementation, in this implementationincludes a dual-core CPU 527 running firmware 526. However, a singlecore or other types of multi-core CPUs may be used in otherimplementations. Generally, a signal conversion block 550, which may bein CPU complex 521, may include a peak detector 529, a web socket 536,firmware stored in memory (“firmware”) 526, and a spectral powerconverter 531. Firmware 526 may receive data from packetizer 511 of FBGA510 into a ring buffer 528 of SoC module 520, which may also be of CPUcomplex 521.

Ring buffer 528 may be used to store a continuous stream of samples frompacketizer 511 of FBGA 510 to in effect allow FOSVC system 500 to plotoutputs of FBG sensors 111 over a period of time. Firmware 526 may beconfigured to clean up data from ring buffer 528. Data from ring buffer528 may be provided to a peak detector 529, and detected peaks may beprovided from peak detector 529 to spectral power block 531 to quantifyspectral power associated with each of such peaks detected. Along thoselines, firmware 526 may quantify wavelength shifts, which are directlyproportional to the amount of strain experienced and spectral powersensed by each FBG sensor 111. This post-processed data 532 may bestored in main memory 523.

In this implementation, programmable gate array 522, which is coupled tomain memory 523, is configured to provide hardware that reads data 532that firmware 526 has placed in main memory 523 and that performs signalprocessing tasks on such data 532 using DSP hardware 525. An example ofa signal processing task may be an FFT and/or the like to measure anyvibration components in data 532.

Output of DSP hardware 525, such as an FFT output for example, may bewritten back to main memory 523 as data 533 for use by CPU complex 521.D/A interface 524 of programmable gate array device 522 may be used tosend FBG sensor data 532 to an external D/A converter 530 to mimic aparametric output of a conventional strain signal conditioner. FOSVCsystem 500 may work as a high-performance “drop-in” replacement for asignal conditioner in conventional strain measurement systems, and soanalog output 502 may be provided to conventional strain measurementinstrumentation (not shown). Each output of D/A converter may representan output of one FBG sensor of FBG sensors 111.

CPU complex 521 via firmware 526 may be configured to read strain data533 that programmable gate array 522 has placed in main memory 523. CPUcomplex 521 may optionally include either or both an Ethernet interface534 or a USB WiFi interface 535 to forward strain data 533 to one ormore remote computers connected over network 590. Optionally, anexternal cloud server 591 may take outputs from multiple FOSVC systems500 and store them in a database for further analysis by softwarerunning on such cloud server 591. In this example, such computers mayinclude multiple HTML5-compliant Web browsers 592 to communicate withcloud server 591 and/or to communicate with one or more FOSVC systems500 to access strain data 533, which may allow users to make businessdecisions and/or configure individual FOSVC systems 500 usingcorresponding optional Web sockets 536 of CPU complexes 521 of suchsystems.

FIG. 6 is a flow diagram depicting an exemplary fiber optic voltageconditioning flow 600. Fiber optic voltage conditioning flow 600 isfurther described in the light of the above-description.

At 601, a light signal may be generated with a laser. At 602, such lightsignal may be received by an optical circulator. At 603, first controlinformation may be generated by a controller coupled to such laser forwavelength-drift control thereof. At 611, TEC and current controlling ofsuch laser may be responsive to first control information generated at603. At 604, second control information may be generated by a dataacquisition module coupled to such controller. Generating second controlinformation at 604 may include generating PID feedback information at612 by such data acquisition module. Generating PID feedback informationat 612 may include recording at 613 by such data acquisition module ofan analog output signal of a photodetector responsive to such analogoutput signal being below at least one of a gain threshold or afrequency threshold therefor. Moreover, PID feedback information mayinclude PID current error information and PID TEC error information.Along those lines, such data acquisition module may add a current setvoltage and a TEC set voltage to such PID current error information andsuch PID TEC error information, respectively, for generating at 604 suchsecond control information.

At 605, such first control information may be adjusted by suchcontroller responsive to such second control information. Such adjustingof such first control information may be to tune wavelength of a laserfor wavelength-drift control of such laser responsive to such secondcontrol information. Wavelength-drift control of such laser may be tocompensate for drift of a Bragg wavelength.

At 606, a returned optical signal may be received by a photodetectorcoupled to such optical circulator. At 607, an analog output signal maybe generated by such photodetector responsive to such returned opticalsignal. Such generating by such data acquisition module of such secondcontrol information at 604 may be for such analog output signalgenerated at 607.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

The foregoing method descriptions and the process flow diagrams areprovided merely as illustrative examples and are not intended to requireor imply that the steps of the various embodiments must be performed inthe order presented. As will be appreciated by one of skill in the artthe order of steps in the foregoing embodiments may be performed in anyorder. Words such as “thereafter,” “then,” “next,” etc. are not intendedto limit the order of the steps; these words are simply used to guidethe reader through the description of the methods. Further, anyreference to claim elements in the singular, for example, using thearticles “a,” “an” or “the” is not to be construed as limiting theelement to the singular.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the invention.

The hardware used to implement the various illustrative logics, logicalblocks, modules, and circuits described in connection with the aspectsdisclosed herein may be implemented or performed with a general purposeprocessor, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor maybe a microprocessor, but, in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. Alternatively, some steps ormethods may be performed by circuitry that is specific to a givenfunction.

In one or more exemplary aspects, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. The steps of a method or algorithm disclosedherein may be embodied in a processor-executable software moduleexecuted which may reside on a non-transitory computer-readable medium.Non-transitory computer-readable media includes any available media thatmay be accessed by a computer. By way of example, and not limitation,such non-transitory computer-readable media may comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that may be used tocarry or store desired program code in the form of instructions or datastructures and that may be accessed by a computer. Disk and disc, asused herein, includes compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media. Additionally, theoperations of a method or algorithm may reside as one or any combinationor set of codes and/or instructions on a non-transitoryprocessor-readable readable medium and/or non-transitorycomputer-readable medium, which may be incorporated into a computerprogram product.

The preceding description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the invention.Various modifications to these embodiments will be readily apparent tothose skilled in the art, and the generic principles defined herein maybe applied to other embodiments without departing from the spirit orscope of the invention. Thus, the invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the following claims and the principles and novelfeatures disclosed herein. Thus, while the foregoing describes exemplaryembodiment(s) in accordance with one or more aspects of the invention,other and further embodiment(s) in accordance with the one or moreaspects of the invention may be devised without departing from the scopethereof, which is determined by the claim(s) that follow and equivalentsthereof. Any trademarks are the property of their respective owners.

What is claimed is:
 1. A system, comprising: a light source; an opticalcirculator coupled to receive a light signal from the light source; afiber grating sensor coupled to the optical circulator to receive thelight signal; a controller coupled to the light source and configured togenerate first control information for wavelength-drift control of thelight source; a data acquisition module coupled to the controller andconfigured to generate second control information for the controller foradjustment of the first control information; a photodetector coupled tothe optical circulator to receive a returned optical signal and coupledto the data acquisition module to provide an output signal thereto; thephotodetector being configured to generate the output signal responsiveto the returned optical signal; an acoustic emission data acquisitionsystem coupled to the photodetector for acoustic emission monitoring;the first control information being for both thermoelectric (“TEC”)tracking and current tracking of the light source for thewavelength-drift control for the output signal to providewavelength-drift compensating for a range from 0 to 20 kHz to providedynamic strain tracking; and the data acquisition module beingconfigured to generate the second control information using the outputsignal.
 2. The system according to claim 1, wherein the data acquisitionmodule is configured to generate proportional-integral-derivative(“PID”) feedback information to generate the second control information.3. The system according to claim 2, wherein the data acquisition moduleis configured to record the output signal of the photodetector beingbelow at least one threshold therefor for generation of the PID feedbackinformation.
 4. The system according to claim 3, wherein the PIDfeedback information includes PID current error information and PID TECerror information.
 5. The system according to claim 4, wherein the dataacquisition module is configured to respectively add a current setvoltage and a TEC set voltage to the PID current error information andthe PID TEC error information for the generation of the second controlinformation.
 6. The system according to claim 1, wherein: thewavelength-drift control of the light source is to compensate for driftof a Bragg wavelength; and the second control information is used toadjust the first control information to tune wavelength of the lightsource for the wavelength-drift control of the light source.
 7. Thesystem according to claim 6, wherein the fiber grating sensor is coupledto the optical circulator to receive the light signal and configured togenerate the returned optical signaling for the wavelength-drift controlfor the output signal.
 8. The system according to claim 7, wherein theoutput signal is a first analog output signal, and wherein the acousticemission data acquisition system is coupled to the photodetector toreceive a second analog output signal therefrom.
 9. The system accordingto claim 8, further comprising: a plurality of photodetectors, aplurality of controllers, a plurality of optical circulators, and aplurality of light sources coupled to the acoustic emission dataacquisition system and configured to generate multi-channel fiber opticvoltage conditioning; and wherein the photodetector, the controller, theoptical circulator, and the light source respectively are of theplurality of photodetectors, the plurality of controllers, the pluralityof optical circulators, and the plurality of light sources.
 10. Thesystem according to claim 9, comprising a plurality of fiber gratingsensors respectively coupled to the plurality of optical circulators toreceive light signals respectively from the plurality of light sourcesand configured to generate returned optical signals respectively fromthe plurality of fiber grating sensors respectively responsive to thelight signals.
 11. The system according to claim 10, wherein theplurality of fiber grating sensors are of a ring multiplexer.
 12. Thesystem according to claim 10, wherein the plurality of fiber gratingsensors are coupled via a star multiplexer.
 13. A method for fiber opticvoltage conditioning, comprising: generating a light signal with a lightsource; receiving the light signal by an optical circulator; receivingthe light signal by a fiber grating sensor coupled to the opticalcirculator; generating first control information by a controller coupledto the light source for wavelength-drift control of the light source;generating second control information by a data acquisition modulecoupled to the controller; adjusting the first control information bythe controller responsive to the second control information; receiving areturned optical signal by a photodetector coupled to the opticalcirculator; generating an output signal by the photodetector responsiveto the returned optical signal; monitoring for acoustic emission by anacoustic emission data acquisition system coupled to the photodetector;and thermoelectric (“TEC”) and current tracking of the light sourceresponsive to the first control information including for thewavelength-drift control for the output signal to providewavelength-drift compensating for a range from 0 to 20 kHz and toprovide dynamic strain tracking, respectively.
 14. The method accordingto claim 13, wherein the generating by the data acquisition module ofthe second control information is for the output signal, the methodfurther comprising: generating proportional-integral-derivative (“PID”)feedback information by the data acquisition module for the generatingof the second control information; and wherein the generating of the PIDfeedback information comprises recording by the data acquisition moduleof the output signal of the photodetector responsive to the outputsignal being below at least one threshold therefor.
 15. The methodaccording to claim 14, wherein the PID feedback information includes PIDcurrent error information and PID TEC error information.
 16. The methodaccording to claim 15, further comprising adding by the data acquisitionmodule a current set voltage and a TEC set voltage to the PID currenterror information and the PID TEC error information, respectively, forthe generating of the second control information.
 17. The methodaccording to claim 13, wherein: the wavelength-drift control of thelight source is to compensate for drift of a Bragg wavelength; and theadjusting of the first control information is to tune wavelength of thelight source for the wavelength-drift control of the light sourceresponsive to the second control information.
 18. A system, comprising:a light source; an optical circulator coupled to receive a light signalfrom the light source; fiber grating sensors coupled to the opticalcirculator to receive the light signal and configured to reflectreflected light back to the optical circulator; a spectral elementcoupled to optical circulator to receive the reflected light andconfigured to provide spectrally dispersed light; a photodiode arraycoupled to receive the spectrally dispersed light and configured todetect the spectrally dispersed light for conversion into analogsignaling; an analog-to-digital converter coupled to receive the analogsignaling and configured to convert the analog signaling into digitalsignaling; a system-on-chip module coupled to receive the digitalsignaling and configured with a peak detector to detect peaks and aspectral power converter to quantify spectral power associated with eachof the detected peaks; and the system-on-chip module configured toquantify wavelength shifts associated the spectral power quantified toprovide strain data.
 19. The system according to claim 18, wherein thesystem-on-chip module comprises digital signal processing circuitryconfigured to perform a Fast Fourier Transform on the strain data toprovide vibration components in the strain data.
 20. The systemaccording to claim 18, further comprising a digital-to-analog convertercoupled to receive and convert the strain data from a digital format toan analog format.